The concept of engine oil heaters is old in the art. In general a heating element is either placed outside of the engine oil pan or into the oil located in the oil reservoir in the engine pan. Because of the problem of thermal breakdown of engine oil the engine oil heaters differ from engine block heaters which heat the engine coolant. Since the coolant does not breakdown under normal heating temperatures, high temperature heating elements can be placed directly in the coolant while heating of engine oil with high temperature heating elements results in breakdown or carbonization of the engine oil.
The prior art oil reservoir heaters that are placed directly in the oil reservoir have two drawbacks. The first is that engine oil heaters, particularly those that operate off the vehicles battery, are of insufficient power to heat the oil to proper temperature to minimize engine wear. In general battery powered heaters have very limited heating life since the battery becomes more inefficient as the temperature of the outside air decreases. On the other hand those prior art heaters that operate off external source may produce such high localized temperatures that the oil around the heating element begins to carbonize or breakdown. In general the temperature at which the oil breaks down varies with the type of oil but in most cases oil breaks down if the temperature is in excess of 300 degrees F. Consequently, such high energy direct contact oil heaters as dipstick heaters are shunned by those who are familiar with the problems that can occur in an engine when the oil breaks down and loses its lubricating qualities. In general if the prior art engine oil heaters don't generate enough heat to produce oil breakdown the heaters usually don't have sufficient heat generation capacity to heat the oil to the proper temperature range to minimize wear on the engine since the engine oil system dissipates heat to the surrounding atmosphere through the engine and the engine oil system.
Another concept of engine oil heaters places an external heater outside the oil pan and then uses a switch or a thermostat to monitor the temperature of the oil or the temperature of the heater. It was believed that such a system would be ideal since the switch or thermostat shuts off the heater when the oil temperature becomes to high thereby preventing the oil from breakdown. Unfortunately, when such thermostatically controlled prior art engine heaters are secured to the exterior of the engine oil pan of heavier surface equipment they have been found to produce insufficient heat or erratic and inconsistent temperature control thereby rendering them ineffective in maintaining the oil temperature of an engine within a prescribed temperature range. It has been found that one of the difficulties, particularly with thermostatically controlled heaters that are secured to the exterior of the engine oil pan of heavier surface equipment, is that either the temperature of the engine oil can not be maintained in a specified range or the heater gradually produces less heat output making it ineffective for maintaining the oil within prescribed limits.
Heating the engine oil to a minimum temperature of about 170 degrees F remains a very desirable goal since hot oil not only makes the engine easier to start in cold climates but also reduces the frictional wear on engine parts thereby prolonging the life of the engine. In most engine applications one wants to maintain the within a temperature range of 170 degrees F to 200 Degrees F to minimize engine wear. It should be understood that if one is increasing the oil temperature only for the purpose of providing starting assistance a lesser oil temperatures could be used since in even the coldest conditions instances heating engine oil up to 60 F is sufficient to start the engine if the battery has not lost its efficiency. However, in extremely cold climates such as encountered in northern climates where the temperature may reach -40 to -50 degrees F. the heating of the oil to a higher temperature also compensates for the loss of efficiency in the battery thus enabling the user to start an engine under the most extreme environmental conditions.
The present invention provides an improved engine oil heater that in the preferred embodiment heats and maintains the oil to a temperature of 180 degrees F. to 200 degrees F. while eliminating the problem of oil breakdown and inconsistent temperature control of the engine oil through a thermal balance heater that has been found to be relatively insensitive to the temperature of the surrounding atmosphere.